JP2016192341A - Titanium-based material for sodium ion secondary battery, manufacturing method thereof, electrode active material using titanium-based material, electrode active material layer, electrode, and sodium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material which is easily combined, does not contain a rare metal and is available for a sodium ion secondary battery.SOLUTION: The material for a sodium ion secondary battery contains at least first group atoms of a periodic table, Ti atoms and O atoms, a ratio of the first group atoms of a periodic table with respect to the Ti atoms (periodic table first group atoms/Ti atoms) is 0.01 to 0.5 (molar ratio) and a ratio of the O atoms with respect to the Ti atoms (O atoms/Ti atoms) is 2.005 to 2.25.SELECTED DRAWING: None

Description

  The present invention relates to a titanium-based material for a sodium ion secondary battery, a method for producing the same, and an electrode active material, an electrode active material layer, an electrode, and a sodium ion secondary battery using the titanium-based material.

  Sodium ion secondary batteries are attracting attention as next-generation secondary batteries that do not use rare metals (Non-Patent Document 1). However, since sodium has a larger ion volume than lithium, graphite most frequently used as a negative electrode material for lithium ion secondary batteries cannot occlude sodium ions. Therefore, conventionally, hard carbon has been mainly cited as a candidate material for a negative electrode material of a sodium ion secondary battery. However, in a secondary battery using such hard carbon as a negative electrode material, capacity and cycle characteristics cannot be sufficiently achieved.

  From such a background, development of a negative electrode material that does not contain a rare metal and has excellent capacity and cycle characteristics is desired.

S. Komaba, W. Murata, T. Ishikawa, N. Yabuuchi, T. Ozeki, T. Nakayama, A. Ogata, K. Gotoh and K. Fujiwara, Adv. Funct. Mater., 21 (20), 3859 ( 2011).

  An object of the present invention is to provide a material that is easy to synthesize, does not contain a rare metal, and can be used for a sodium ion secondary battery.

  As a result of intensive investigations in view of the above-mentioned object, a substance having Ti atoms is added to an aqueous alkali solution having a specific concentration, heated to 60 to 450 ° C., and alkali is replaced with hydrogen atoms as necessary, followed by heating. Thus, the inventors have found that a specific titanium-based structure is obtained, and that the above-described problem can be solved by employing this titanium-based structure. The inventors of the present invention conducted further research and completed the present invention.

  That is, this invention includes the following structures.

  Item 1. It contains at least periodic group 1 atom, Ti atom and O atom, and the ratio of periodic group 1 atom to Ti atom (periodic group 1 atom / Ti atom) is 0.01 to 0.5 (molar ratio). And the ratio of O atoms to Ti atoms (O atoms / Ti atoms) is 2.005 to 2.25.

Item 2. Item 2. The material for a sodium ion secondary battery according to Item 1, wherein the average minimum size is 1 to 100 nm and the specific surface area is 10 m ² / g or more.

  Item 3. Item 3. The material for a sodium ion secondary battery according to Item 1 or 2, wherein the ratio of H atom, Li atom, Na atom, K atom in Group 1 atoms of the periodic table is 99 mol% or more.

  Item 4. Item 4. The material for a sodium ion secondary battery according to any one of Items 1 to 3, wherein a ratio of H atoms in Group 1 atoms of the periodic table is 50 mol% or more.

  Item 5. Item 5. The material for a sodium ion secondary battery according to any one of Items 1 to 4, wherein the total of Na and K contained is 5% by weight or less.

  Item 6. Item 1 is a solid fiber shape, rod shape, belt shape, hollow fiber shape, tube shape, a sheet-like substance having a thickness of 10 nm or less, or a roll around which the sheet-like substance is wound. The material for sodium ion secondary batteries in any one of -5.

Item 7. The method for producing a sodium ion secondary battery material according to any one of Items 1 to 6,
(1) A production method comprising a step of alkali-treating a material containing at least titanium at 160 to 450 ° C. for 1 hour or more in an alkaline aqueous solution of 2 to 20 mol / L.

  Item 8. Item 8. The method according to Item 7, wherein the material containing at least titanium is metal titanium, titanium oxide, titanium hydroxide, titanium alkoxide, titanium trichloride, titanium tetrachloride, titanium sulfate, titanyl sulfate, and titanium nitrate.

  Item 9. The material containing at least titanium is titanium oxide, titanium hydroxide, titanium tetramethoxide, titanium tetraethoxide, titanium tetra n-propoxide, titanium tetraisopropoxide, titanium tetra n-butoxide, titanium tetra s-butoxide, Item 9. The method according to Item 7 or 8, which is at least one selected from the group consisting of titanium tetra-t-butoxide.

  Item 10. Item 10. The production method according to any one of Items 7 to 9, wherein the material containing at least titanium contains titanium oxide or titanium hydroxide having a thickness of 50 nm or less.

  Item 11. Item 11. The production method according to any one of Items 7 to 10, wherein the alkali contains sodium hydroxide and / or potassium hydroxide and / or lithium hydroxide.

  Item 12. Item 12. The method according to any one of Items 7 to 11, wherein the alkali contains at least 50% by weight of sodium hydroxide.

Item 13. further,
(2) The production method according to any one of Items 7 to 12, comprising a step of substituting hydrogen (H) for Group 1 atoms of the periodic table other than hydrogen present in the material obtained in step (1). .

  Item 14. Item 14. The manufacturing method according to Item 13, wherein the step (2) is a step of bringing the solution containing an acidic compound into contact with the material obtained in the step (1).

  Item 15. Item 15. The method according to Item 14, wherein the solution containing the acidic compound is an aqueous solution containing at least one selected from the group consisting of hydrochloric acid, nitric acid, and acetic acid.

Item 16. further,
(3) The manufacturing method according to any one of Items 13 to 15, further comprising a step of heat-treating the titanium-based structure obtained in the step (2) at 200 to 500 ° C. for 0.5 to 24 hours.

  Item 17. Item 17. The method according to Item 16, comprising a step of performing heat treatment at 250 to 350 ° C for 1 to 15 hours.

  Item 18. The sodium ion secondary battery material according to any one of Items 1 to 6 or the sodium ion secondary battery material obtained by the production method according to any one of Items 7 to 17 A negative electrode active material layer for a secondary battery.

  Item 19. A negative electrode for a sodium ion secondary battery, comprising the negative electrode current collector and the negative electrode active material layer for a sodium ion secondary battery according to Item 18.

  Item 20. An electricity storage device comprising the negative electrode for a sodium ion secondary battery according to Item 19.

  ADVANTAGE OF THE INVENTION According to this invention, the titanium type sodium ion secondary battery material applicable to a sodium ion secondary battery and its simple manufacturing method can be provided. This titanium-based material exhibits a high discharge capacity and excellent cycle characteristics when employed in a titanium-based sodium ion secondary battery.

1. Titanium-based material The material for a sodium ion secondary battery of the present invention includes at least a periodic table group 1 atom, a Ti atom, and an O atom, and a ratio of the periodic table group 1 atom to a Ti atom (periodic group 1 atom). / Ti atom) is 0.01 to 0.5 (molar ratio), and the ratio of O atom to Ti atom (O atom / Ti atom) is 2.005 to 2.25. That is, although it is not titanium oxide (TiO ₂ ), titanium oxide may be mixed, and the ratio is preferably 10% by weight or less.

In the titanium-based structure of the present invention, the ratio of group 1 atom of the periodic table to Ti atom (period group 1 atom / Ti atom; molar ratio) is 0.01 to 0.5, preferably 0.1 to 0.1. 0.35. If the ratio of group 1 atom of the periodic table to Ti atom is less than 0.01, the chemical structure is close to TiO ₂ and the cycle characteristics may be deteriorated. Moreover, when the ratio of the periodic table group 1 atom to the Ti atom exceeds 0.5, the charge / discharge capacity and the cycle characteristics are deteriorated. Further, the ratio of the group 1 atom of the periodic table to the Ti atom is not necessarily a single substance having an integer ratio, and a mixture of structures having different ratios may be used.

  In the titanium-based structure of the present invention, the ratio of O atom to Ti atom (O atom / Ti atom; molar ratio) is 2.005 to 2.25, preferably 2.05 to 2.2. When the ratio of O atoms to Ti atoms is less than 2.005, the cycle characteristics may be deteriorated. On the other hand, when the ratio of O atoms to Ti atoms exceeds 2.25, the charge / discharge capacity and the cycle characteristics deteriorate.

  Examples of the periodic table Group 1 atoms of the titanium-based material of the present invention include H atoms, Li atoms, Na atoms, and K atoms. In addition, although the one where content of Na and K in the titanium-type material of this invention is large is easy to synthesize | combine, the one where it reduces can improve charge / discharge capacity and cycling characteristics more. Specifically, the content of Na and K in the titanium-based material is preferably 5% by weight or less of the total weight of the titanium-based material, and more preferably 3% by weight or less.

  From such a viewpoint, it is preferable that the periodic table Group 1 atom contained in the titanium-based structure of the present invention contains 50 mol% or more (70 to 100 mol%, particularly 90 to 100 mol%) of H atoms.

  In addition, content of periodic table group 1 atom, Ti atom, O atom, etc. shall be measured by fluorescent X-ray (WDX), X-ray diffraction (XRD), TG-DTA, ICP, ion chromatography, etc.

It is preferable from the viewpoint of rate characteristics that the average minimum size is 1 to 100 nm and the specific surface area is 10 m ² / g or more. As the average minimum size is smaller and the specific surface area is larger, the rate characteristics are better, while aggregation is more likely to occur. On the other hand, when the average minimum size is large in the range of 1 to 100 nm and the specific surface area is small in the range of 10 m ² / g, dispersion during electrode production becomes easy.

  In the present invention, the “average minimum size” of the titanium-based material is, for example, an average diameter and an average length in the case of a solid fiber shape, rod shape, belt shape, hollow fiber shape, or tube shape. In the case of a sheet shape or a roll shape formed by winding a sheet, it means the smallest one of average width, average thickness, and average length. That is, the “average minimum size” of the titanium-based material means the smallest dimension among the dimensions of the titanium-based material.

  The shape (average minimum size, average diameter, average width, average length, and average aspect ratio) of the titanium-based material is measured, for example, by observation with an electron microscope (SEM or TEM), and the cross section is, for example, FIB (Focused Ion). After processing by Beam), it shall be observed by TEM.

The specific surface area of the titanium-based material of the present invention is preferably 10 m ² / g or more, more preferably 15 m ² / g or more. When the specific surface area is 10 m ² / g or more, the contact area with the electrolytic solution is large, and a rapid decrease in reactivity with the electrolytic solution is suppressed, so that deterioration of rate characteristics can be prevented. On the other hand, to facilitate dispersion during electrode fabrication suppress more shrinkage of the coating film, from the viewpoint of further preventing cracks, the specific surface area is preferably 500 meters 2 / ^g or less, more preferably 420 m 2 / ^g. The specific surface area is measured by the BET method or the like.

2. Method for producing titanium-based material <Step (1)>
The titanium-based structure of the present invention is, for example,
(1) In a 2-20 mol / L alkaline aqueous solution, it can manufacture by the method provided with the process of alkali-treating the material containing at least titanium at 60-450 degreeC for 1 hour or more.

  In step (1), although not limited thereto, a material containing at least titanium and an aqueous alkali solution of 2 to 20 mol / L may be heated to 60 to 450 ° C. and left or stirred for 1 hour or more. preferable.

  Specifically, an alkali metal hydroxide is added to a dispersion (for example, an aqueous dispersion or the like) of a material containing at least titanium (in particular, an aqueous dispersion of titanium oxide or a titanium oxide precursor) so as to have the above concentration. It is preferable to put in, heat to 60 to 450 ° C., and leave or stir for 1 hour or more. In addition, the specific method is not limited to this, and a material containing at least titanium (particularly titanium oxide or a titanium oxide precursor) or a dispersion thereof (particularly titanium oxide or oxidation) in a 2 to 20 mol / L aqueous alkali solution. An aqueous dispersion of a titanium precursor) may be added, heated to 60 to 450 ° C., and allowed to stand for 1 hour or longer.

  The aqueous alkaline solution is preferably an aqueous solution in which an alkali, particularly an alkali metal hydroxide (sodium hydroxide, potassium hydroxide, lithium hydroxide, etc.) is dissolved. Especially, it is preferable that sodium hydroxide and / or potassium hydroxide are included.

  As the alkaline aqueous solution, an aqueous solution of an alkali metal hydroxide is preferable from the viewpoint of dissolving the surface of a raw material containing titanium (particularly titanium oxide or a titanium oxide precursor) and promoting the reaction. In addition, it is good also as an aqueous solution containing 2 or more types of alkalis as an alkali, for example, it is also possible to use sodium hydroxide as a main component and to use potassium hydroxide, lithium hydroxide, etc. together.

  The concentration of the alkaline aqueous solution is 2 to 20 mol / L, preferably about 3 to 20 mol / L, more preferably about 5 to 15 mol / L. When the concentration of the aqueous alkali solution is less than 2 mol / L, the material containing titanium as a raw material is difficult to dissolve, the reaction does not proceed sufficiently, or the reaction rate becomes extremely slow. On the other hand, when the concentration of the aqueous alkali solution exceeds 20 mol / L, there may be a problem in production such as a high viscosity of the reaction solution and a large amount of waste solution generated after synthesis.

  Although there is no restriction | limiting in particular as a material containing titanium to be used, A titanium oxide or a titanium oxide precursor is preferable. Specifically, titanium metal, titanium oxide, titanium hydroxide, titanium alkoxide, titanium trichloride, titanium tetrachloride, titanium sulfate, titanyl sulfate, and titanium nitrate can be used. Known or commercially available titanium oxide fine particles may be used as they are, or titanium hydroxide may be used. In addition, titanium halide, titanium alkoxide, or the like that generates titanium hydroxide by contact with water may be used. These materials containing titanium may be used alone or in combination of two or more.

  Among these, from the viewpoint of purity, titanium oxide, titanium hydroxide, titanium tetramethoxide, titanium tetraethoxide, titanium tetra n-propoxide, titanium tetraiso, which have no Ti, O, H or alcohol structure. Propoxide, titanium tetra n-butoxide, titanium tetra s-butoxide, and titanium tetra t-butoxide are preferred.

  The average particle diameter of the raw material is preferably 50 nm or less. Titanium alkoxide is preferable in the sense that when it comes into contact with water, nanoparticles having an average particle size of 50 nm or less are formed. The lower limit of the average particle diameter of the titanium oxide or titanium hydroxide is not particularly limited, but is usually about 1 nm. The average particle diameter of titanium oxide is measured by observation with an electron microscope (SEM or TEM).

  The amount of the material containing titanium to be charged into the alkaline aqueous solution is not particularly limited, but is preferably 0.1 to 20% by weight with respect to water from the viewpoint of balancing the fluidity and productivity of the reaction solution, 0.5-10 weight% is more preferable.

  Moreover, the form of the material containing titanium is not particularly limited. For example, an aqueous dispersion of a material containing titanium or an aqueous sol of a material containing titanium may be used. Further, a material containing titanium may be put into an alkaline aqueous solution as it is.

  The process temperature of a process (1) is 60-450 degreeC, Preferably it is 60-300 degreeC, More preferably, it is 80-250 degreeC. The higher the temperature, the shorter the reaction time, and the average minimum size tends to increase when compared at the same reaction time. Conversely, when the reaction is performed at a low temperature, a titanium-based material having a large specific surface area and a small average minimum size is likely to be generated.

  There is no restriction | limiting in particular in the time of the said alkali treatment, About 0.1 to 100 hours are preferable, About 1 to 24 hours are more preferable from a viewpoint of progress of reaction and productivity. The smaller the raw material containing titanium and the higher the concentration of the alkaline aqueous solution, the shorter the reaction time.

In place of step (1), titanium oxide or a titanium oxide precursor and sodium salt such as NaOH, KOH, Na ₂ CO ₃ , K ₂ CO ₃ are heat-treated at 500 ° C. to 1000 ° C. to obtain fine sodium titanate, or Potassium titanate may be formed. In this method, the specific surface area does not increase and is at most 30 m ² / g.

<Step (2)>
Carbodihydrazide, methyl carbazate As a method of replacing sodium (Na) and / or potassium (K) with hydrogen (H), the titanium-based structure obtained in step (1) can be prepared with a solution containing an acidic compound. It is preferable to make it contact.

  Specifically, it is preferable to immerse the titanium-based structure obtained in step (1) in a solution containing an acidic compound. Specifically, the titanium-based structure may be directly charged into a solution containing an acidic compound, or a dispersion of a titanium-based structure and a solution containing an acidic compound may be mixed. From the viewpoint of uniformly dispersing the titanium-based structure in the solution containing the acidic compound, it is preferable to prepare a dispersion of the titanium-based structure in advance and mix this with the solution containing the acidic compound. In addition, in order to promote dispersion | distribution in the case of immersion, time can be shortened if dispersion | distribution operation by stirring, an ultrasonic wave, etc. is performed.

  As the acidic compound, a protonic acid compound that can exchange alkali metal ions and protons and can be easily removed later, has a small molecular weight and is easily volatilized or decomposed is preferable. Specific examples include aqueous solutions of common inorganic acids or organic acids such as hydrochloric acid, nitric acid, acetic acid, oxalic acid, sulfuric acid, hydrofluoric acid, formic acid, and more preferably hydrochloric acid, nitric acid, acetic acid, oxalic acid. Etc. These acids can be used alone or in combination of two or more.

  Moreover, the buffer solution which contains an acidic compound and the conjugate base of this acidic compound can also be used for the solution containing the said acidic compound. Specific examples include a buffer solution containing acetic acid and sodium acetate.

  In addition, when using the solution containing an acidic compound, it is preferable after this process to wash the titanium-based material with water to remove the acid and the liberated metal salt.

  The time for contacting with the solution containing the acidic compound is preferably about 0.1 to 168 hours under atmospheric pressure conditions, and more preferably 1 hour or more when it is necessary to sufficiently remove the alkali metal.

  Further, the method for replacing sodium (Na) and / or potassium (K) with lithium (Li) is not particularly limited, but (1) a method in which a titanium-based structure is brought into contact with an aqueous lithium salt solution, and (2) titanium. Examples thereof include a method of bringing a system structure into contact with a lithium-based molten salt, and (3) a method of heat-treating a titanium-based structure and a lithium salt in a dry state. In the methods (1) and (2), the titanium-based structure may be used as it is or as a dispersion. In any of these methods, sodium (Na) and / or potassium (K) can be directly substituted with lithium (Li), or once substituted with hydrogen (H) and further substituted with lithium (Li). You can also.

In the method (1), for example, the titanium-based structure is preferably contacted by mixing (immersing) with an aqueous solution of LiCl, LiOH, LiNO ₃ or the like.

In the method (2), for example, it is preferable that the mixture is brought into contact, for example, by melting a mixture of two or more of LiOH, LiNO ₃ , LiCl and the like at 250 to 1000 ° C. and mixing (immersing) with a titanium structure. .

In the method (3), for example, it is preferable to mix a titanium-based structure with LiCO ₃ , LiOH or the like and perform heat treatment at 400 to 1000 ° C.

<Step (3)>
In the method for producing a titanium-based material of the present invention, after the above step (2),
(3) It is preferable to include a step of heat-treating the titanium-based structure obtained in step (2) at 200 to 500 ° C.

  The heat treatment temperature is preferably 200 to 450 ° C. in the gas phase and more preferably 250 to 350 ° C. from the viewpoint that the Ti—OH group remaining in the titanium-based structure is dehydrated and is not completely converted to TiO 2. preferable. In addition, there is no restriction | limiting in particular as atmosphere in the case of heat-processing in a gaseous phase, Air atmosphere, nitrogen atmosphere, argon atmosphere, etc. are preferable. Further, it may be under reduced pressure such as vacuum.

  The heat treatment may be performed in a normal gas phase or in vacuum, but may be performed in a liquid phase. When carried out in the liquid phase, the crystallinity can be increased at a low processing temperature, so it may be carried out at 100 to 400 ° C, more preferably 120 to 350 ° C, and even more preferably 150 to 300 ° C.

  The titanium-based material obtained in this way has the characteristics described in the above “1. Titanium oxide material”.

3. Electrode active material layer The electrode active material of the present invention contains the titanium-based material of the present invention. In the present invention, the electrode active material layer contains an electrode active material containing the titanium-based material of the present invention.

  Moreover, in this invention, you may use together with the negative electrode active material conventionally used for the sodium ion secondary battery as another negative electrode active material in an electrode active material layer.

  Examples of negative electrode active materials that can be used in combination include non-graphitizable carbon (hard carbon), silicon-based materials such as Si and SiO, other titanium-based materials such as lithium titanate, metal oxides such as tin oxide, Al , Si, Pb, Sn, Zn, Cd, etc. and an alloy compound of sodium and the like can be used. These negative electrode active materials may be used individually by 1 type, and may be used in combination of 2 or more type.

  The ratio of the titanium-based material of the present invention and the other electrode active material in the electrode active material layer of the present invention is not particularly limited. However, the present invention is effective for all active materials in terms of both safety and charge / discharge capacity. The titanium-based structure of the invention is preferably 50 to 100% by weight, more preferably 70 to 100% by weight.

  In addition to the above active material, the electrode active material layer may contain a known conductive material, binder, and the like. Examples of the conductive material include acetylene black, ketjen black, carbon black, graphite, carbon nanotubes, carbon nanofibers, graphene, and amorphous carbon obtained by heat treating an organic substance. As the binder, for example, fluorinated resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene rubber, acrylonitrile butadiene rubber ( NBR), polyacrylonitrile, polyimide, ethylene-vinyl alcohol copolymer resin (EVOH), ethylene-propylene-diene rubber (EPDM), polyurethane, polyacrylic acid, polyamide, polyacrylic acid ester, polyvinyl ether, carboxymethylcellulose sodium Salt, carboxymethylcellulose ammonium, hydroxypropylcellulose, hydroxyethylcellulose, modified cellulose such as methylcellulose and cellulose nanofiber It may also be mentioned.

  The mixing ratio of the electrode active material, the conductive material and the binder in the electrode active material layer is not particularly limited, but the electrode active material is preferably 30 to 99% by weight, and 40 to 95% by weight from the viewpoint of achieving both capacity and conductivity. % Is more preferable. Further, the conductive material is preferably 1 to 50% by weight, and more preferably 2 to 40% by weight. Further, the binder is preferably 1 to 30% by weight, and more preferably 3 to 20% by weight.

  The titanium-based material of the present invention is a nanomaterial having a large specific surface area as described above. Other active materials, conductive materials, binders, and the like are particulate or powder materials. Therefore, when these are mixed to form an electrode active material layer paste, it is preferable to form a paste by mixing an organic solvent such as water, alcohols, acetone, N-methylpyrrolidone, dimethyl sulfoxide, or dimethylformamide. .

  The thickness of the electrode active material layer of the present invention is preferably 5 to 200 μm, more preferably 10 to 150 μm, from the viewpoint of securing sufficient capacity and electrode strength.

  The electrode active material layer of the present invention as described above can be formed by molding and drying the electrode active material layer paste formed as described above.

4). Sodium ion secondary battery The sodium ion secondary battery of the present invention comprises the negative electrode for the sodium ion secondary battery of the present invention, and the positive electrode and the negative electrode are installed via a separator, and nonaqueous electrolysis is performed between the positive electrode and the negative electrode. It is preferable to fill the liquid. Specifically, it is preferable to install the positive electrode and the negative electrode through a separator impregnated with a nonaqueous electrolytic solution.

The positive electrode may be any material that can supply sodium to the negative electrode, and a known positive electrode material can be used. In particular, when aiming at a high-capacity sodium ion secondary battery, it is possible to supply sodium equivalent to a charge / discharge capacity of 150 mAh or more per gram of negative electrode material in a steady state (for example, after repeated charge / discharge about 5 times). Preferably there is. More preferably, a material capable of supplying sodium equivalent to a charge / discharge capacity of 180 mAh or more, more preferably 200 mAh or more is used. For example, a composite metal oxidation represented by the general formula NaMO ₂ or Na ₄ M ₃ (PO ₄ ) ₂ P ₂ O ₇ (wherein three M are the same or different and each represents Cr, Co or Ni). In particular, an intercalation compound containing Na is preferable, and better characteristics can be obtained particularly when NaCrO ₂ , Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ or the like is used. These positive electrode active materials may be used individually by 1 type, and may be used in combination of 2 or more type.

  As the conductive material and the binder, those described above can be used.

  As the non-aqueous electrolyte, an organic electrolyte containing an organic solvent and an electrolyte salt is preferable.

  Examples of organic solvents for the organic electrolyte include low-viscosity chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; cyclic carbonates with high dielectric constant such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; γ -Butyrolactone; 1,2-dimethoxyethane; tetrahydrofuran; 2-methyltetrahydrofuran; 1-3 dioxolane; methyl acetate; methylpropionate; dimethylformamide; sulfolane; triglyme; tetraglyme; . Moreover, when seeking heat resistance, you may use various molten salts (ionic liquid), such as an imidazolium salt. Of these, ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate and the like are preferable.

As the electrolyte salt is not particularly limited, for _{example, NaClO 4, NaAsF 6, NaPF} 6, NaBF 4, NaB (C 6 H 5) 4, CH 3 SO 3 Na, CF 3 SO 3 Na, NaCl, NaBr Etc. are preferred.

  As the separator, a microporous membrane made of a polyolefin resin such as polyethylene is used, which is formed by laminating a plurality of microporous membranes having different materials, weight average molecular weights and porosity, and various plastic films on these microporous membranes. It may be one containing an appropriate amount of additives such as an agent, an antioxidant, and a flame retardant. In addition, since the dendrites hardly occur in the titanium-based structure of the present invention, a normal resin mesh or cellulose film can also be used.

  As the shape of the electricity storage device, a wound oval shape, a circular shape, or the like can be used. Other constituent elements of the battery include a terminal, an insulating plate, a battery case, and the like. Conventionally, these components can be used as they are.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited only to these.

Example 1
2 g of 16 nm titanium oxide nanoparticles were put into a solution (NaOH concentration 28.6% by weight) mixed with 100 g of water and 40 g of NaOH, sealed in a Hastelloy pressure vessel, and held at 200 ° C. for 12 hours.

  The resulting material was added to 2000 g of water and filtered. 10 g of acetic acid and 100 g of water were added to the filtrate and stirred for 24 hours. Thereafter, filtration and dispersion in 1000 g of water were repeated to finally obtain 2.2 g of a white substance.

  This material was heated in vacuum at 200 ° C. for 3 hours and in air at 300 ° C. for 5 hours to give 2 g of white material.

When observed by SEM, a belt-like substance having an average width of 70 nm and an average length in the longitudinal direction of 2.5 μm was observed. Moreover, it was 35 m < ² > / g when the BET specific surface area was measured. Further, when the Na content was examined by fluorescent X-ray (WDX), it was 0.1% by weight.

Example 2
2 g of 16 nm titanium oxide nanoparticles were put into a solution (NaOH concentration 28.6% by weight) mixed with 100 g of water and 40 g of NaOH, sealed in a Hastelloy pressure vessel, and held at 200 ° C. for 12 hours.

  The resulting material was added to 2000 g of water and filtered. Further, filtration and dispersion in 1000 g of water were repeated to finally obtain 2.4 g of a white substance.

  This material was heated in vacuum at 200 ° C. for 3 hours and in air at 300 ° C. for 5 hours to give 2.2 g of white material.

When observed by SEM, a belt-like substance having an average width of 70 nm and an average length in the longitudinal direction of 2.5 μm was observed. Moreover, it was 30 m < ² > / g when the BET specific surface area was measured. Further, when the Na content was examined by fluorescent X-ray (WDX), it was 4% by weight.

Example 3
5 g of 16 nm titanium oxide nanoparticles were put into a solution in which 100 g of water and 40 g of NaOH were mixed (NaOH concentration 28.6% by weight), and kept at 120 ° C. for 12 hours in a stainless steel container.

  The resulting material was added to 2000 g of water and filtered. 50 g of acetic acid and 20 g of water were added to the filtrate and stirred for 48 hours. Thereafter, filtration and dispersion in 1000 g of water were repeated to finally obtain 2.2 g of a white substance.

  This material was heated in vacuum at 200 ° C. for 3 hours and in air at 300 ° C. for 5 hours to give 2 g of white material.

When observed by TEM, a structure in which sheets having a thickness of about 1 nm and a width of 200 to 2000 nm were aggregated was observed. Moreover, it was 230 m < ² > / g when the BET specific surface area was measured. Further, when the Na content was examined by fluorescent X-ray (WDX), it was 0.3% by weight.

Example 4
5 g of 16 nm titanium oxide nanoparticles were put into a solution in which 100 g of water and 40 g of NaOH were mixed (NaOH concentration 28.6% by weight), and kept at 120 ° C. for 12 hours in a stainless steel container.

  The resulting material was added to 2000 g of water and filtered. Further, filtration and dispersion in 1000 g of water were repeated to finally obtain 2.4 g of a white substance.

  This material was heated in vacuum at 200 ° C. for 3 hours and in air at 300 ° C. for 5 hours to give 2 g of white material.

When observed by TEM, a structure in which sheets having a thickness of about 1 nm and a width of 200 to 2000 nm were aggregated was observed. Moreover, it was 195 m < ² > / g when the BET specific surface area was measured. Further, when the Na content was examined by fluorescent X-ray (WDX), it was 7.7% by weight.

Experimental example 1
Acetone was added to and kneaded with 4.5 g of the titanium-based material synthesized in Example 1, 4.0 g of acetylene black, and 1.5 g of PTFE powder, molded with a biaxial roll, and dried at 170 ° C. in a vacuum. The obtained sheet was bonded to an aluminum foil to produce an electrode. A charge / discharge test was conducted under the conditions of 50 mA / g, 2.67 V-0.1 V (vs Na / Na ⁺ ) using NaPF ₆ (EC / DEC mixed solvent) with Na metal and 1 mol / L electrolyte as a counter electrode. It was.

as a result,
Cycle 6: charge capacity 169 mAh / g, discharge capacity 150 mAh / g
Cycle 11: charge capacity 170 mAh / g, discharge capacity 159 mAh / g
With each cycle, the discharge capacity increased.

Experimental example 2
A cell was prepared from the titanium-based material synthesized in Example 2 in the same manner as in Experimental Example 1, and 1 to 10 cycles were charged and discharged under the condition of 2.67 V-0.67 V (vs Na / Na ⁺ ). From the 11th cycle, a charge / discharge test was conducted under the condition of 2.67 V-0.1 V (vs Na / Na ⁺ ).

as a result,
Cycle 11: charge capacity 304 mAh / g, discharge capacity 216 mAh / g
A high discharge capacity was observed.

Experimental example 3
The titanium-based material synthesized in Example 3 was tested in the same manner as in Experimental Example 1.

as a result,
Cycle 1: Discharge capacity 240 mAh / g
Cycle 5: discharge capacity 217 mAh / g
A high discharge capacity was observed.

Experimental Example 4
The titanium-based material synthesized in Example 4 was tested in the same manner as in Experimental Example 1.

as a result,
Cycle 1: Discharge capacity 185 mAh / g
Cycle 5: discharge capacity 189 mAh / g
Cycle 10: Discharge capacity 198 mAh / g
With each cycle, the discharge capacity increased.

Experimental Example 5
The experiment was performed in the same manner as in Experimental Example 4 except that the titanium-based material synthesized in Example 4 was changed to 12.5 mA / g only in the charge / discharge conditions.

as a result,
Cycle 1: Discharge capacity 208 mAh / g
Cycle 2: Discharge capacity 204 mAh / g
A high discharge capacity was observed.

Comparative Example 1
The test was performed in the same manner as in Experimental Example 1 except that the titanium-based material was changed to lithium titanate (Li ₄ Ti ₅ O ₁₂ ).

as a result,
Cycle 5: discharge capacity 130 mAh / g
Cycle 10: Discharge capacity 125 mAh / g
Compared with Experimental Examples 1 to 5, the discharge capacity was low.

Claims (20)

  It contains at least periodic group 1 atom, Ti atom and O atom, and the ratio of periodic group 1 atom to Ti atom (periodic group 1 atom / Ti atom) is 0.01 to 0.5 (molar ratio). And the ratio of O atoms to Ti atoms (O atoms / Ti atoms) is 2.005 to 2.25. The material for sodium ion secondary batteries according to claim 1, wherein the average minimum size is 1 to 100 nm, and the specific surface area is 10 m ² / g or more.   The material for sodium ion secondary batteries according to claim 1 or 2, wherein a ratio of H atom, Li atom, Na atom, K atom in the group 1 atom of the periodic table is 99 mol% or more.   The material for a sodium ion secondary battery according to any one of claims 1 to 3, wherein a ratio of H atoms in Group 1 atoms of the periodic table is 50 mol% or more.   The material for sodium ion secondary batteries according to any one of claims 1 to 4, wherein the total of Na and K contained is 5% by weight or less.   The shape is a solid fiber shape, rod shape, belt shape, hollow fiber shape, tube shape, or a sheet-like material having a thickness of 10 nm or less or a roll shape around which the sheet-like material is wound. The material for sodium ion secondary batteries in any one of -5. It is a manufacturing method of the material for sodium ion secondary batteries in any one of Claims 1-6,
(1) A production method comprising a step of alkali-treating a material containing at least titanium at 160 to 450 ° C. for 1 hour or more in an alkaline aqueous solution of 2 to 20 mol / L.   The manufacturing method according to claim 7, wherein the material containing at least titanium is metal titanium, titanium oxide, titanium hydroxide, titanium alkoxide, titanium trichloride, titanium tetrachloride, titanium sulfate, titanyl sulfate, and titanium nitrate.   The material containing at least titanium is titanium oxide, titanium hydroxide, titanium tetramethoxide, titanium tetraethoxide, titanium tetra n-propoxide, titanium tetraisopropoxide, titanium tetra n-butoxide, titanium tetra s-butoxide, The production method according to claim 7 or 8, which is at least one selected from the group consisting of titanium tetra-t-butoxide.   The manufacturing method according to claim 7, wherein the material containing at least titanium contains titanium oxide or titanium hydroxide having a thickness of 50 nm or less.   The manufacturing method in any one of Claims 7-10 in which the said alkali contains sodium hydroxide and / or potassium hydroxide, and / or lithium hydroxide.   The manufacturing method in any one of Claims 7-11 in which the said alkali contains 50 weight% or more of sodium hydroxide at least. further,
(2) The production method according to any one of claims 7 to 12, comprising a step of substituting hydrogen (H) for Group 1 atoms of the periodic table other than hydrogen present in the material obtained in step (1). .   The manufacturing method according to claim 13, wherein the step (2) is a step of bringing a solution containing an acidic compound into contact with the material obtained in the step (1).   The manufacturing method according to claim 14, wherein the solution containing the acidic compound is an aqueous solution containing at least one selected from the group consisting of hydrochloric acid, nitric acid, and acetic acid. further,
(3) The manufacturing method in any one of Claims 13-15 provided with the process of heat-processing the titanium-type structure obtained at process (2) at 200-500 degreeC for 0.5 to 24 hours.   The manufacturing method of Claim 16 provided with the process of heat-processing at 250-350 degreeC for 1 hour-15 hours.   A sodium ion secondary battery material according to any one of claims 1 to 6, or a sodium ion secondary battery material obtained by the production method according to any one of claims 7 to 17. A negative electrode active material layer for a secondary battery.   A negative electrode for a sodium ion secondary battery, comprising the negative electrode current collector and the negative electrode active material layer for a sodium ion secondary battery according to claim 18.   An electricity storage device comprising the negative electrode for a sodium ion secondary battery according to claim 19.